Rahm Emanuel is the latest Obama aide to quit – with more expected to follow

Rahm Emanuel, White House Chief of Staff for two years, will announce his resignation today to run for Mayor of Chicago. To take immediate effect, his departure is only the latest in a gathering exodus of aides and counsellors to President Barack Obama at the very moment that he is facing the greatest political peril.

Confirming the latest round of West Wing musical chairs, White House sources said last night that Mr Emanuel will be replaced, at least on an interim basis, by Pete Rouse, a loyal Obama lieutenant who is well known and widely liked in Washington, including on Capitol Hill, but whose public profile is very low.

"The President will have a personnel announcement to make," a coy White House spokesman, Robert Gibbs, told reporters while refusing to elaborate further. "You can bet on having two announcements."

Mr Rouse was once chief of staff to the former Senate majority leader Tom Daschle. However, he joined Mr Obama's team when he was first elected to the US Senate and followed him to the White House upon his presidential victory in 2008. The appointment of Mr Rouse may disappoint some Democrats who had been looking to Mr Obama to use Mr Emanuel's departure as an opportunity to bring new blood into his circle.

But the strong standing of Mr Rouse on Capitol Hill could prove valuable to the President, particularly if he goes into the second half of his term with diminished leverage in Congress with most polls expecting an end to the Democrat majority in the House of Representatives in congressional elections on 2 November.

Mr Obama is already searching for a replacement for his top economic adviser, Larry Summers, who headed for the exits earlier this month, while speculation has grown that General Jim Jones, the National Security Adviser, will also opt to leave the Obama circle before the end of this year.

That Mr Emanuel was considering relinquishing his perch at the White House has been hot gossip in Washington since Richard Daley, the long-serving Mayor of Chicago, shocked many three weeks ago by announcing he would not be running for re-election next year, thus lowering the curtain on the Daley dynasty that has run America's third-largest metropolis for much of the last five decades. His father was mayor before him.

Mr Emanuel has always had a reputation for plain speaking and hard arm-twisting. His work for President Obama saw many successes, not least finally steering healthcare reform through deeply reluctant Democratic ranks on Capitol Hill last year. But he leaves a boss who is contemplating steep losses in the November mid-term elections and suffering from deeply depressed approval numbers.